The present invention relates generally to a client/server system for measuring and displaying color density of documents (including images) located on remote file servers wherein access occurs over a local or wide area network such as the Internet based World Wide Web (WWW).
A basic function of World Wide Web browsers in common use today, such as Netscape Navigator and Microsoft Internet Explorer, is to allow web pages stored on a remote Web server to be retrieved and viewed. The user initiates a viewing session on a web browser by specifying a particular URL corresponding to a page to be viewed. The web server transmits the various elements of the requested page to the browsing application. Any special data formats, e.g., video, audio, certain images, documents not written in HTML language, etc., are treated by one or more web browser software plug-ins on the client computer.
A common need is to be able to view digital images on the client computer and be able to read, display and record color density measurements over wide area networks or the Internet. The digital images are stored on image servers located somewhere in the network and are not stored on the user""s local computer. In addition, it would be useful if the system were able to aid the user in interpreting the color measurement readings to match a specific printing system with a particular color book. Note that the users of the system may be located anywhere in the world as long they have a connection to the wide area network, e.g., the Internet.
In the printing and graphic arts industry, printed color is measured utilizing tools known as densitometers. Color is measured for many reasons, a major reason being tocalibrate printers used in the printing process so that the printed color can be matched to an original item or a known standard. When the printed data is still in digital form it is common practice in the printing and graphic arts fields to measure color values in the digital image by means of software that functions to emulate the physical device for measuring color, the software being typically provided with the image editing and display systems.
This electronic densitometer allows the gray level of each of the color components to be measured at a specific coordinate location in the image. The measured color values may be expressed in the form of component color values, e.g., cyan (C), magenta (M), yellow (Y) and black (K), for each color component, i.e., separation, present in the measured color image. Alternatively, the measured color values may be expressed as composite color space vectors that represent the color space coordinates of the measured color at a location being measured. The color space vectors are color space coordinates within a system-independent coordinate system such as CIE XYZ or L*, a*, b*.
Spot colors, i.e., special colors, such as gold, silver or those used in color systems like Pantone(copyright) or Toyo may also be represented. Since the computer based video display systems represent the image using the RGB color space, it is far more preferable to measure color using the original color channels from the digital image file. This ensures that the correct values are presented to the user, i.e., before they are converted to RGB.
A problem arises, however, when a digital image is subject to color space transformations such as a conversion from the CMYK color space to CIELab or RGB. When conversions are used, it is highly likely that the resulting densitometer readings are not the same as they would be using the original color data. This is due to the fact that the color values are rounded during the conversion calculations introducing errors and that the transformations themselves are not reversible.
The problem is further compounded when the images are compressed before being transmitted to the client workstation over a network such as a WAN or the Internet. In this case, it is difficult to measure color on images that are compressed because the color space of the images typically changes as part of the compression algorithm. Thus, color information cannot be reliably or accurately measured at the client site receiving the compressed images.
In addition, a problem with current systems is that the color viewed on the screen is not sufficient to provide accurate density data on the underlying image. The ability to measure color of an image displayed on screen is very useful when working with an image that is ultimately to be printed. In the pre-press phase of generating printed images, it is very helpful to be able to measure the spot color of an image in any desired location. This information is used in conjunction with a color book to view the actual colors that will be printed when the image goes to press.
In currently available imaging systems, however, color density readings are made directly from an off-screen memory that is located within the user workstation where the image is viewed. Thus, the off-screen memory in the user image workstation holds the entire original image that may be 10, 50, 100 MB or more. Alternatively, the original images are located on a file system wherein both the file system and the image workstation are connected to a high speed local area network. In the case where off-screen memory is used to store the original image, color readings are made directly from the off-screen memory where the image is stored. In the case where a file system connected to a LAN is used to store the image, color readings are made directly from the image file server.
An example of a commercially available product is widely used Adobe Photoshop(copyright) application program. This software program incorporates a digital color densitometer feature that functions to read color values at a specific coordinate of the image. This tool, however, reads the pixel color value information from off screen memory that holds a copy of the original image.
In another example, the Scitex Prismax retouching workstation is an image processing workstation designed for the graphic arts industry. The workstation incorporates a digital color densitometer that functions to read and display color component values at a specific image coordinate. Unlike Adobe Photoshop, however, this system samples the original image that resides on an image file server connected to a LAN.
A disadvantage of the prior art densitometer systems is that they are not suitable for use with large images where the user image workstation and the original image are either not co-located in the same device or are not connected by a high speed LAN. In particular, the prior art systems are not practical for use with user image workstations that are connected to image file servers over low rate connections such 28.8, 33.6 or 56 Kbps dial up access over the Internet.
In addition, the prior art systems are not client/server solutions whereby multiple users can simultaneously access the same image. Further, these systems do not permit users to work directly with printing press references such as reference color books. Some prior art systems compress the image in memory so that the image takes up less memory to store or the image is decompressed with the result that the decompressed image is not the same as the original. In this case, color densitometer readings are not from the original image but from some altered version of the original image.
For example, in prior art systems color density measurements are taken from a local frame buffer containing color data in RGB color space. The color data is converted into CMYK values using one of several well-known conversion techniques for converting color from the RGB color space to CMYK. This process, however, is not accurate due to the conversion between color spaces that is required.
In addition, it would be desirable to record densitometer readings as annotations on the image itself for use by others. More than one densitometer reading should be able to be displayed over the image. Others viewing the document would then be able to view the densitometer notes as well. Prior art systems do not permit a user to record multiple densitometer readings and have them displayed with the image itself along with the ability to share them with other viewers.
Thus, there is a strong felt need for a densitometer system that is client/server based and able to measure color density at any point in the original image and display the readings on the user image workstation and to display any associated color book information in addition thereto.
The present invention is a client/server system for reading, measuring and displaying color density of documents (including images) located on a remote file system and accessed over a WAN such as the Internet. The color density information displayed corresponds to specific coordinates of documents located on the remote image file servers. The invention provides means for reading, displaying and recording color density measurements of digital images that are not stored on the user""s local computer. The invention allows for measuring color using a compressed version of a document where the color values displayed on screen are not accurate and may or may not be stored in off-screen memory. Note that the system of the present invention is also suitable for use with black and white images as well as color. References to color images throughout this document are intended to encompass black and white images as well.
The invention can be implemented as software, a portion of which executes on the server side and a portion executes on the client side. The server side may comprise a plurality of software applications running in parallel that in combination provide the server functionality of the invention. A web server application on the server side functions to capture special requests from one or more client applications for measuring, sending, recording and retrieving color density measurements related to specific positions of specific documents located in the image filer server.
The color density information is transmitted between client and server applications via TCP/IP protocols over communications means such as a LAN, WAN or the Internet. The invention may be adapted to operate over an Intranet, e.g., LAN, or Extranet, e.g., WAN or the Internet.
On the client side a client software application functions to display the document that the user wishes to read color density information from and provides the tools necessary to permit the user to measure, send, record and retrieve color density measurements. Note that the client software application can be implemented as a web browser plug-in module. The plug-in contains the user interface for navigating within the document and for handling the color density measurements.
A color densitometer button is provided which, when pressed by the user, displays the densitometer floating window for showing the measurements. For example, when the user presses the left mouse button at a specific image coordinate on the screen, the server measures the color density value at the corresponding coordinate in the original document file. The color density information is transmitted back to the client and subsequently displayed in the floating densitometer window.
The client is capable of receiving the color density information in any one of a various number of color spaces. Additional information regarding spot colors and position in a digital color book can also be displayed as requested by the user. Further, the user can record the results of the color density measurement by pressing an annotation button in the color densitometer window. In response, a note containing the results, i.e., the color values, is created and placed over the image in the same location as the-color density reading.
A synchronization button is also provided which, when pressed by the user, transmits any previously recorded color density measurement annotations generated by the user from the client to the server using a suitable communications protocol. In response, the server transmits back an acknowledgement along with any new record notes that other clients may have posted since the last synchronization was performed.
Multiple users may measure color density of a document at the same time. Each individual user may measure color density values of many documents at the same time. This is achieved by the user opening several web browser windows, one for each document color density measurements are to be taken.
In accordance with the invention, the color density measurement readings are transmitted from the server independent of the data transmitted that is related to the viewed document The server first checks that a user is authorized before replying with color measurements. At the client side, the client application layers the color measurement reading records over the document (image) in accordance with the coordinates of each.
A key feature of the present invention is the ability of a user to refer to a printed color book which the user can use to match image colors displayed in RGB color space on the computer monitor screen with the CMYK image colors subsequently produced by the target printing process. The server functions to provide the exact location of the measured color in the particular color book being used. Using the same digital source file, i.e., digital color book, one or more color books may be printed. Each color book represents a single instance of a variety of different printing machines, color inks, paper stock and varying printing conditions. Any number of color books can be used at the client side for reference purposes by a user. Thus, the invention helps in interpreting the color density readings to match the nuances of a specific printing system by means of a color book.
As result, the present invention has the advantage of permitting multiple clients to measure, send, record and retrieve color density information of a document. This is achieved by measuring the color density values of documents that reside on a centralized web server. Note that the multiple clients perform color density measurements on one or more documents in an asynchronous fashion.
When color density annotations are posted to the server by a client, the state of the annotation database stored therein is synchronized such that all other clients can retrieve the current, up to date color density annotations associated with a document.
The densitometer measurement system of the present invention is applicable to numerous types of fields including the printing and graphic arts industry, medical industry and graphical information systems (GIS). It is also applicable to professionals in various fields including, for example, color printers (e.g., offset, gravure, flexo), service bureaus, graphic designers, doctors, cartographers and illustrators, trade shop personnel and anyone having a need to verify the correctness of colors and/or measure and verify colors in a document displayed on the monitor screen. In addition, in order for a user to specify changes in color to portions of a document, it is necessary to be able to retrieve the original color values in the original digital image.
The present invention functions to retrieve the color density information directly from the original document itself without requiring any conversions from one color space to another, e.g., RGB to CMYK. It is important to point out that the densitometer system of the invention does not read color data from a local off-screen buffer or from a file that is local to the system or client computer. Rather, the invention is operative to read and retrieve color density information from the original document file via a WAN such as the Internet. The invention is intended to operate over WAN links that may be relatively slow, e.g., 28.8, 33.6, 56 or 64 Kbps.
There is thus provided in accordance with the present invention a client/server based color density measurement system comprising an original document stored in a document file in an image database on a server coupled to a network, the document file for storing a digital representation of a document, one or more clients coupled to the network, each client operative to locally display a representation of the original document remotely stored on the server in the document file, the client adapted to permit a user to measure color density of the original document at a specific coordinate location and the server operative to measure color density information from the original document in response to a request received from a client over the network, the server sending via the network the results of the color density measurement to the client for display to the user.
The system further comprises means for measuring and displaying color density information relating to spot colors and their CMYK equivalent used within the original document, means for recording color density measurement results in a note subsequently associated with the original document file, means for calculating an entry in a color book whereby a color patch in the color book is selected that corresponds to the color density measurement results returned by the server.
The server and the client comprise means for measuring color density information of an original document that has not yet been fully displayed by the client. The server is adapted to vary the number of pixels used to measure the color density in accordance with the ratio between the number of pixels displayed on a monitor associated with the client and the corresponding number of pixels in the original document stored on the server. The client is adapted to display the results of the color density measurement with an indication that the result is not accurate in the event the zoom factor is other than 1:1. The client is adapted to display an indication of the transparency of a particular color separation or element of the document.
The client comprises a computer display monitor, network communication means, a processor suitably programmed to run a web browser application and a client plug-in adapted to run within the web browser, the client plug-in operative to locally display a representation of the original document remotely stored on the server in the document file and to permit a user to measure and display color density of the original document at a specific coordinate location.
The server comprises network communication means, a processor suitably programmed to provide web server services, provide densitometer agent services and to measure color density information from the original document in response to a request received from a client over the network, the server sending via the network the results of the color density measurement to the client for display to the user.
The system server is adapted to receive the color density measurement requests from the one or more clients and respond to the requests utilizing the Hypertext Transport Protocol (HTTP). The system further comprises security means for providing Universal Resource Locator (URL) translation and redirection services so as to provide user level security for documents and notes stored on the server.
There is also provided in accordance with the present invention, in a client/server system coupled to a network, a method of measuring the color density of a document comprising the steps of storing an original document as a digital representation of a document in a document file in an image database on a server coupled to a network, displaying locally a representation of the original document remotely stored on the server in the document file on a client wherein one or more clients are coupled to the network, accepting a request from a user to measure color density of the original document at a specific coordinate location, the server measuring color density information from the original document in response to the request received from a client over the network, the server sending via the network the results of the color density measurement to the client for display to the user.
The method further comprises the step of measuring and displaying color density information relating to spot colors and their CMYK equivalent used within the original document, the step of recording color density measurement results in a note subsequently associated with the original document file, the step of the client calculating an entry in a color book whereby a color patch in the color book is selected that corresponds to the color density measurement results returned by the server and the step of the server calculating an entry in a color book whereby a color patch in the color book is selected that corresponds to the color density measurement results returned by the server.
The step of displaying locally a representation of the original document on the client comprises transmitting either a non-compressed or a compressed document from the server to the client.